The present invention relates to a novel undercoating composition for photolithographic patterning on a substrate surface or, more particularly, to a coating composition for forming an undercoating layer between the surface of a substrate and a photoresist layer with an object to efficiently prevent reflection of the exposure light on the substrate surface with good conformability and good workability in coating works even to a substrate surface having stepped level differences as well as little sublimation of the ingredients at an elevated temperature encountered during processing.
It is a remarkable trend in recent years in the technology of semiconductor devices that, along with the increasing degree of integration in the semiconductor devices, ultraviolet lights of shorter and shorter wavelengths are used for pattern-wise exposure of the photoresist layer in the photolithographic patterning so that the major current of the photolithographic patterning technology is now in the use of the i-line light of 365 nm wavelength, deep ultraviolet light and excimer laser beams. One of the serious problems accompanying the use of the above mentioned short-wavelength ultraviolet lights is reflection of the exposure light on the substrate surface because the reflecting light necessarily passes through the photoresist layer resulting in local deformation or so-called notching of the pattern formed in the resist layer and degradation in the dimensional accuracy of the resist pattern formed by the photolithographic patterning. Accordingly, it is a measure now under development as a remedy of this drawback that a reflection-preventing undercoating layer is interposed between the substrate surface and the photoresist layer formed thereon. Various types of reflection-preventing undercoating compositions have been proposed for this method, referred to as the BARC (bottom anti-reflective coating) method.
While the principal object heretofore in the use of a BARC composition in photolithographic patterning is to accomplish a higher degree of reflection preventing effect, the undercoating composition for the BARC method is required to have excellent conformability even to a substrate surface having stepped level differences. Further, the undercoating composition is required to exhibit a high selectivity ratio in etching between the undercoating layer and the photoresist layer thereon or, namely, the ratio of the etching rate of the undercoating layer to that of the photoresist layer thereon.
Besides the above mentioned selectivity ratio, a BARC composition is required to exhibit excellent workability in coating works to give an undercoating layer of high uniformity without being influenced by the gas flow caused by the nitrogen flashing of or exhaust gas discharge from the heat-treatment furnace which may cause unevenness in the coating layer.
A further problem to be taken into consideration in the formulation of a BARC composition is sublimation of the ingredients. While the coating composition is compounded usually with an ultraviolet absorbing agent with an object to enhance the anti-reflective effect, namely, many of conventional ultraviolet absorbing compounds more or less have sublimability so that, when the undercoating composition is compounded with such a sublimable ultraviolet absorbing compound, the compound sometimes is sublimated and deposited in the course of the photolithographic patterning process on the inner walls of the treatment chambers or ovens so as to greatly disturb the succeeding processes. Therefore, it is very important that any of the ingredients in the undercoating composition exhibit no or little sublimation at an elevated temperature of processing.